The storage of volatile, toxic fluids has long presented a safety and environmental hazard. Aviation fuel is among the most volatile of liquids and is stored in large quantities throughout the country. Underground storage tanks have been used in the aviation industry for the storage of fuel and other highly volatile liquids, but such tanks have serious drawbacks, in that their construction and maintenance are expensive, and owing to their lack of mobility. Recently, underground storage tanks have come under attack on environmental grounds, as it is difficult to determine when the tank has been ruptured or damaged so as to permit volatile, and often toxic, materials to escape and pollute the environment.
In the aviation industry flammable liquids, including fuel having a comparatively low vapor pressure, have been stored in above-ground storage tanks which are vented to the atmosphere. In the event such a flammable liquid gets excessively warm while in a storage tank, it produces considerable vapor within the tank, the pressure of which can readily be relieved, in an above-ground tank, to prevent the tank from rupturing.
Relatively small vents are usually provided in a storage tank to take care of normal atmospheric changes. To handle the large quantity of vapor produced by a flammable liquid under excessive heating, it is important that the tank be relieved with a sufficiently large area vent, to prevent rupture.
Above-ground fuel storage tanks for holding volatile or toxic liquids would be desirable, but existing tanks of this type have their own attendant shortcomings.
Vapors of a stored liquid can condense on an outside surface of the tank upon passing through the vents, owing to a temperature differential between the interior and exterior of the tank. Such condensation of relatively low volatility liquids, mechanical rupture in the case of flammable liquid, and corrosion, in the case of all types of liquids, can result in uncontrolled dripping or leaking of the liquid on the outside surface of the storage tank. Uncontrolled leaks can also result from the overflow of a flammable liquid through the vents when a storage tank is overfilled.
The results of such uncontrolled leaks are: penetration of the body of the storage tank, leading to the interruption of use of the storage facility until the necessary repairs can be made; the fire hazard represented by an uncontrolled pool of highly flammable liquid in the near vicinity of the storage tank; the health hazard of having toxic liquids seep into the soil, possibly finding their way into the food chain or water supplies; and the financial loss resulting from the loss of expensive liquid.
Above-ground tanks must provide for avoiding environmental pollution resulting from damage to the tank and escape of the contents. A further problem with above-ground fuel storage tanks is that they are also subject to exposure to the elements, must be constructed to avoid overflow of the contents due to expansion as a result of heating), and must contend with corrosion and contamination from rain, snow and other environmental factors.
It is an object of the present invention to provide an above-ground liquid storage system which is safe, inexpensive to construct and maintain, and relatively mobile.
Another object of the invention is to provide a storage system for liquid in which the development of leaks, including leaks due to an overflow of liquid through the vents and leaks resulting from condensation of vapors passing through the vents of the tank, will not result in the loss of the liquid.
An important object of the present invention is to provide a liquid storage tank which can collect and recover liquid which may leak from the tank.
It is a further object of the present invention to provide an above-ground fuel storage tank that avoids the inspection problems inherent in underground storage tanks but provides means for protecting against escape of the contents due to corrosion, rupture of the tank wall, leakage or expansion of the liquid in the tank, thereby avoiding pollution or contamination of the environment.
A liquid storage system in accordance with the present invention includes an external containment vessel which is open on top and an internal storage tank mounted within the external containment vessel so as to extend above it. The internal tank and the containment vessel are constructed and arranged so as to have a substantial outer storage space formed between them. This storage space is covered by a roof structure which extends from a point below the top of the internal storage tank to cover the containment vessel. A venting structure is provided at a location on the internal tank above the roof structure, where it is exposed to the atmosphere, and a drainage structure provides liquid coupling from the venting structure to the outer storage space.